The long-term objective of the project is to identify a theory of timing that accounts quantitatively for many measures of behavior in many procedures used in the study of time perception and timed performance. These include procedures that involve classical conditioning, operant conditioning, and choice. The times of individual responses (lever pressing, head entry into the food cup, and licks on a water tube) will be recorded, and will be the basis for determination of the characteristics of bouts of responses, overall response rates, and the relationship between events (stimuli, responses, and reinforcers) and the local response rate. Rats will be trained in comparable timing procedures that differ in the number of stimuli and response contingencies, the distribution of food reinforcers, and the average rate of reinforcement. The hypothesis is that the bout structure is relatively stable, the overall response rate is largely controlled by the overall rate of reinforcement, and the pattern of responding is largely controlled by the expected time to reinforcement. A packet theory of timing is being developed that may account quantitatively for the results. It will be evaluated with respect to its simplicity, flexibility, and generality, as well as its fit to the behavioral data. The original data will be made available on the web so that others may verify, challenge, and/or extend published results and to compare alternative explanations of the data. Various distortions of time perception are characteristic of different psychiatric disorders and drug induced disorders. An understanding of the mechanisms underlying timed performance may contribute to an understanding of these effects.